1. Field of the Invention
The present invention relates to a gas fuel heater and in particular to a heater mounted to a pressure regulator and having a thermostatic control that is responsive to the gas temperature to control the flow of engine coolant through the heater.
2. Description of Related Art
Compressed natural gas, when used as a vehicle fuel, is stored at very high pressures, typically greater than 3000 psi. The vehicle engine cannot utilize the fuel at this high pressure. Thus, a pressure reducing regulator is needed to lower the gas fuel pressure. A single stage regulator is more desirable than a multiple stage regulator due to the simplicity of the design. During the pressure reduction, as the gas expands, the temperature of the gas decreases. This expansion of gas can yield gas temperatures near or below xe2x88x92100xc2x0 C. This cooling effect of the gas is most notable in the preferred single-stage regulator design. The single-stage regulator manufactured by ITT Conoflow is designed to expand the gas outside the body of the regulator so that the regulator itself is not subjected to the extreme cold of the expanding gas.
The gas fuel metering valve on the engine, however, must have gas at a temperature above 40xc2x0 C. and preferably above 0xc2x0 C. to avoid freezing of any moisture in the fuel line. When this pressure reducing regulator is used in close proximity to the engine, there is insufficient ambient heating of the gas in the fuel line connecting the regulator to the metering valve, on the engine to warm the fuel to the desire temperature. A heater is needed to raise the temperature of the expanded gas above the minimum temperature required by the fuel metering valve.
The present invention provides a natural gas heater that is thermostatically controlled. The heater housing is coupled to the body of the regulator. The heater is connected to the engine cooling system and receives engine coolant that flows through a coolant passage in the heater. The heater has a gas passage therein with a gas inlet and outlet. The heater gas inlet is in communication with the gas outlet of the regulator via an external pipe.
The heater housing is cylindrical and has a core therein that separates the gas and coolant passages. The core includes a cylindrical wall having radially outwardly extending fins in the gas passage and radially inward extending fins in the coolant passage. The outwardly extending fins are truncated at alternating axial ends, forming a serpentine gas passage around the fins. The cylindrical housing has a gas inlet and a gas outlet circumferentially spaced apart from one another. A pair of fins separate the gas inlet from the gas outlet, providing a insulating air space between the inlet and the outlet.
Engine coolant flows through the center of the core to provide heat to the core and the radially outward extending fins in the gas passage. A thermostat is provided to close the coolant passage when the gas is overheated. The thermostat is controlled by a wax reservoir located in the gas passage adjacent the gas outlet. The thermostat thus responds to the gas temperature to open and close the coolant passage.
Since the heater is attached externally to the regulator body as opposed to being integrally formed with the regulator body, if the regulator is used in a vehicle configuration where sufficient ambient heating of the gas fuel is available between the regulator and the engine, the heater can simply be eliminated and the fuel line to the engine coupled to the gas outlet of the regulator body.
In preferred embodiments, the gas fuel is regulated to 110 psi or 120 psi and is warmed to about 90xc2x0 F. The heater of the present invention can be used with gaseous fuels other than natural gas that are stored at high pressures and are excessively cooled when the pressure is reduced in a single stage regulator.